Amorphous aromatic polyesters are well known in the polymeric art. They are generally characterized by the repeating unit carboxy ester ##STR1## Aromatic polyesters are of particular importance and have many useful applications. Examples of aromatic amorphous polyesters for this invention include polycarbonates, copolyestercarbonates, polyarylates and polycycloalkylene phthalates.
Generally speaking aromatic polycarbonate resins offer a high resistance to the attack of mineral acids, may be easily molded, are physiologically harmless as well as strain resistant. It is also well known that polycarbonate resins have high impact strength below a critical thickness of between about 1/8 and 1/4 inch. Additionally polycarbonates are transparent and process at relatively high temperatures with the appropriate melt viscosities.
Copolyestercarbonates are generally quite similar to polycarbonate in properties but generally have a higher secondary transition temperature (Tg) than the comparable polycarbonates. Polyarylates are generally quite similar to the copolyestercarbonates in properties but have a still higher secondary transition temperature than the copolyestercarbonates.
Common to all these amorphous aromatic polyesters are the rather high processing temperatures accompanied by the relatively high melt viscosities. This is particularly true of the polycarbonates, copolyestercarbonates and polyarylates. Many processing aids have been introduced to lower the processing temperature and melt viscosities. However, all of them meet with some undesired effects. The polystyrenes have been used as processing upgraders, however the amorphous aromatic polyesters generally loose their tensile elongation and oftentimes will also become embrittled when polystyrenes are present. Other properties which can be affected are the clarity and the appearance of the molded part.
It has now been discovered that the addition of a carboxy terminated polystyrene oligomer lowers melt viscosity and essentially maintains to a significant extent a substantial number of its other properties such as flexural and tensile measurements as well as DTUL and impact resistance. Although the structure(s) of the composition is not known with certainty it is believed that ester interchange occurs to some extent between the carboxy terminated polystyrene and the amorphous aromatic polyester, thereby forming a new molecule. It is also believed that present in the new composition is an intimate admixture of the two components.